The present invention is directed to a thermochromic temperature sensitive composition used to detect the prevailing temperature, and particularly, to detect when the temperature is within a particular range. When the temperature is within that range, the composition undergoes a color change that is visible to the observer.
Though compositions which provide an indication of the prevailing temperature are known in the art, and exemplary compositions are described below, these compositions have not shown themselves to be satisfactory in all instances, and in any event, there is always a need to improve over the existing compositions, and to simplify the way in which they operate. For instance, known devices may be of a relatively complicated assembly or construction, in that the material which provides the physical indication of the prevailing temperature, which ordinarily may be a dye or pigment, is isolated in a compartment contained within the housing of the device. Also, the dye or pigment may not be temperature sensitive (thermochromic) per se, in that the material may change color based upon the change in another physical parameter, such as pH. Another drawback is that the devices, by virtue of the indicating material, may indicate only a given temperature, which may not be the temperature range desired by the end user.
The present invention seeks to rectify these shortcomings.
U.S. Pat. No. 5,857,776 discloses a method and a device for monitoring the handling conditions of at least one object intended to be handled under certain predetermined conditions. The temperature or the temperature as a function of time of at least one object, is monitored to enable it to retain as much as possible of its original quality. To this end, a device is inserted into the object, or between two objects in a stack of objects, including a substantially flat, elongate casing, having a slot-shaped space between two opposed walls of the casing. An elongate slide-shaped body removably inserts into the slot-shaped space of the casing. At one end the slide-shaped body is provided with a technique for indicating, by color change, the absence or presence of predetermined conditions. The color change is thereafter observed visually by withdrawing the body that is removably inserted in the slot-shaped space of the casing. During the visual observation, the color may be suitably compared with a color scale on the slide-shaped body. Also, the casing of the device may be perforated at one end. Furthermore, at least the portion of the inside of the casing contacting the means when inserted in the casing, may be suitably provided with ridges extending in the longitudinal direction of the casing. The device includes a temperature sensitive composition which undergoes a pH shift upon freezing.
U.S. Pat. No. 5,788,375 discloses a floating cooking indicator, comprising first and second layers with a thermochromic material disposed therebetween, the first layer being transparent to permit viewing of the thermochromic material and the second layer including a plastic material with lower density particles dispersed therein.
U.S. Pat. No. 5,779,364 discloses a temperature indicator utilizing waxes, low-temperature melt metals or polymers attached to a support member that will melt to reveal a visible indicia on the support member thereby serving as an indicator that the product container to which the invention is attached has been heated beyond a predetermined stable temperature of the product.
U.S. Pat. No. 5,695,284 discloses a thaw indicator unit for sensing and permanently recording a thawing experienced by a temperature sensitive food or other item. The unit has a container of transparent, non-toxic material with a hermetically sealed chamber containing a frozen color change medium having at least two segments of differently colored frozen aqueous compositions, the segments being juxtaposed along an interface of molecular thickness, and at least one of the segments being substantially homogeneously colored differently from at least one juxtaposed other colored segment, wherein the colorants are food grade materials, and whereby the unit when placed on, in or in close proximity to the item will record any first thawing by way of thawing of the juxtaposed segments and intermixing thereof at least at the interface thereof to produce at least a visible section of an intermix of said compositions and having a markedly different and readily visible color from that of the juxtaposed segments.
U.S. Pat. No. 5,254,473 discloses an indicator composition and process capable of changing color in relationship to its exposure to a temperature above and below a base line temperature and to the time of the exposure. The indicator is deposited as a layer on the substrate, which comprises a dispersion of either a binder comprising a reaction inert, neutral finely divided absorbent, in the presence of a reactant comprising a salt of an acid or an organic compound substituted by at least one moiety which, in ionic form, is an anion or a binder/reactant, comprising at least one solid organic polymer whose constituent units contain, as a covalent substituent, at least one moiety which, in ionic form, is an anion. The indicator composition is at least one acid sensitive pH dye. The activator is at least one base. This composition and process may be utilized to form a solid state device for monitoring integral values of time and temperature during storage of perishables.
U.S. Pat. No. 5,215,378 discloses a dual temperature indicator providing visual indications when exposed to predetermined high or low temperatures. The indicator has a bulb with a capillary tube and an attached high temperature indicator structure. The bulb has a first liquid which also fills a predetermined portion of the tube. A separating substance and a second miscible liquid further fills a predetermined portion of the remainder of the tube. At a predetermined low temperature, the liquid in the bulb contracts causing the separating substance and a portion of the second liquid to move into the bulb to produce a visible color change. The high temperature indicator structure has an indicating member in contact with the capillary tube end and which provides a visual indication at a predetermined high temperature when the liquids expand upon an environmental temperature increase.
U.S. Pat. No. 4,892,677 discloses a process for producing articles useful in monitoring the time-temperature history of perishable items. The process initially involves forming a solution comprised of a diacetylenic monomer and a solvent. The solution is frozen, and the frozen solution having crystalline diacetylenic monomer therein is irradiated to partially polymerize the diacetylenic monomer. Partial polymerization of the crystalline diacetylenic monomer admixed with frozen solvent results in the production of a novel article of manufacture having color. The novel article of manufacture is comprised of frozen solvent, diacetylenic monomer, and colored polydiacetylene. Due to the intensity of the color of the polydiacetylene, the entire article of manufacture appears to be colored. The colored article of manufacture may be attached to various perishables to monitor the shelf fife of the perishables. Upon exposure to temperatures above a critical temperature, the frozen solvent melts and extracts unreached monomer from the colored polymer, thereby causing a sharp color transition which indicates that the perishable should possibly be discarded.
U.S. Pat. No. 4,829,539 discloses a temperature indicating device which comprises a plurality of panels in a fixed array. Some of the panels are adapted to undergo a reversible change in appearance at a given temperature whereas the remainder are adapted to undergo irreversible change in appearance at a given temperature. The device is useful in indicating the temperature of an object as well as its actual temperature.
U.S. Pat. No. 4,468,137 discloses a temperature indicating device comprising a series of liquid crystal cells each of which contains a liquid crystal material having a different composition, the composition varying from cell-to-cell, and each of which cells exhibits the grandjean state whereby temperature is indicated by iridescence of the cells, the cells being such that the liquid crystal material in each has a clearing point at a different selected temperature in a series of temperature in a temperature range of interest and that each of the cells is such that its liquid crystal material does not revert immediately to the grandjean state on cooling from the isotropic liquid state wherein the improvement comprises the cells having a construction such that the liquid crystal material of each cell undergoes, on cooling from the isotropic liquid state, the transition isotropic liquid state to focal conic state, without reverting immediately to the grandjean state.
U.S. Pat. No. 4,457,252 discloses a critical temperature indicator utilizing the volume reduction characteristics of organic compounds as they undergo a change from the liquid state to the solid state. The bulb and a portion of the capillary tube of a thermometer-like structure contains a colorless organic compound. Another organic compound saturated with a dye, which compound has a solidification temperature lower than that of the colorless compound and which is miscible with the colorless compound, is located in the capillary tube and separated from the colorless compound by a solid, movable plug or a liquid which is immiscible with either the colorless or the dyed compound. The volume of the colorless compound upon solidification is less than the volume of the bulb so that the separating plug or liquid and at least a portion of the dyed compound are drawn into the bulb upon solidification. The dyed compound then mixes with the colorless compound to provide a visual indication that the colorless compound has solidified.
U.S. Pat. No. 4,299,727 discloses a disposable, reversible thermometer. The thermometer comprises (1) a suitable heat-sensitive composition; (2) a suitable matrix-forming amorphous material; and (3) a suitable film-forming material that is more crystalline than the matrix-forming amorphous compound.
The principle object of the present invention is to provide a temperature sensing composition that provides visual indication of the temperature in the prevailing environment.
It is a further object to provide a temperature sensing composition that is relatively simple to construct and use.
It is a further object of the invention to provide a temperature sensing composition that possesses a unitary construction.
The invention is a temperature sensing composition comprised of a thermochromic dye, which is dispersed or dissolved in a plastic resin. The resin can be a thermoset such as an epoxy, a polyurethane, a phenolic or other thermoset, or it can be a thermoplastic such as polyethylene, polypropylene, a polyvinyl chloride, a polyester or other thermoplastic. The temperature sensing dye changes from colorless to a deep color as the temperature falls below 45 degrees Fahrenheit. The exact temperature of change can be anywhere between 35 and 45 degrees Fahrenheit depending on the specific thermochromic dye that is used. As described herein, it should be understood that the composition is non-discreet, or in other words, the composition is of an integral construction, as the thermochromic dye is dispersed in the resin.
The invention can be used as an indicator that indicates when the temperature of a refrigerator or other food storage container rises above 40 to 45 degrees Fahrenheit, which is the optimum temperature range for storage of food. The material can be applied to a painted or unpainted plastic, ceramic, glass or metal substrate which is then placed in the refrigerator. Alternatively, the material can be applied directly to the refrigerator wall or shelf. It can also be applied to the refrigerator as a magnetic strip.
The invention can also be used with outdoor faucets and valves to indicate that the freezing point is approaching. For instance, it can be applied directly to the valve or faucet, or the material can be coated on a metal, ceramic, glass or plastic substrate, which can be attached to the valve or faucet. In a further embodiment, the present invention is constructed as a flange that is affixed to the exterior of attached to the outside of an outdoor faucet and notifies the observer whether water in the line is approaching the freezing point. The material can also be used as a warning method for bridge surfaces or airplane wings, which are subject to freezing temperature in cold weather. The material can be applied directly to all or a part of the bridge or wing structure or surface, or it can be coated on a metal, ceramic, glass or plastic substrate to provide a visible warning device. The material serves as an alert to the approach of freezing of the bridge or wing surface. The device could also be used by farmers or the like to sense and warn of oncoming frost or other cold temperatures that could damage crops.
It has been observed that the present invention can sense the differences in the temperature of air currents that flow over the device, and thus is very sensitive to temperature differentials. Specifically, a wave-like pattern visible as a transient color change that flows across the body of the device has been observed when the air current flowing over the device has a temperature above or below 42xc2x0 F. This indicates that the device is capable of indicating the prevailing temperature in localized regions, with satisfactory degree of precision.
None of the temperature indicators disclosed in the prior art references cited above provide a means for sensing temperatures as disclosed in the present invention in which a thermosensitive, (i.e.xe2x80x94thermochromic) dye is dispersed in a matrix forming resin material. When a particular threshold temperature is reached, the dye component undergoes a reversible color change, that is visible in the temperature sensing composition, informing an observer of a pending temperature change.